Blower Motor could be bad. Can be tested by unplugging, then hooking directly to 12v battery.
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Check the connectors on the front of the heater box for pin damage from overheating. Common problem. There are usually visual "burny marks and meltyness" (author: ratmonkey)
Looks something like this...

Some cut the connectors out and splice all the wires together.
Or just bypass the connector with damaged wires spliced together.